It is known in the art to design circuits parts that are especially important for the function redundantly or partly redundantly in order to improve the general reliability in operation of circuit arrangements for control units. In the simplest case, the entire circuit is designed fully redundantly, hence is duplicated, and subjected to a more or less distinct spatial/physical separation so that errors will concern, if at all, only one of the duplicated circuit parts. It is a disadvantage in this procedure that frequently the expenditure in cost, the space required, and the current consumption is doubled as well. To process safety-critical signals, it is customary to use two analog-to-digital converters for redundancy reasons. Herein below, the entire analog/digital interface will be referred to as an analog-to-digital converter, that means, including analog multiplexers at the input as well as result registers and (digital) multiplexers at the output of the analog-to-digital converter.